This invention relates generally to a control system for a water heater with an external heat source. More particularly, it is directed to a control system for a conventional domestic hot water heater in association with an external heat source which may take the form of a heat pump.
A conventional domestic hot water heater typically includes an internal heat source in the form of a tank heating unit having an electric heating element and a tank thermostat. When the thermostat indicates a demand for hot water, the tank heating unit is turned on. When the thermostat indicates that the demand for hot water has been satisfied, the tank heating unit is turned off.
The heat pump has been known for many years. Although it is generally more economical to operate than a conventional tank heating unit, it has not been used extensively heretofore because power, particularly electric power, has been inexpensive. As the cost of power increases, there is renewed interest in the use of a heat pump in association with a water heater, particularly for providing domestic hot water.
When a heat pump is used with a hot water heater, it would be advantageous if its control system were responsive to the tank thermostat as an indicator of the demand for hot water. Such an arrangement is disclosed in Shaffer et al U.S. application Ser. No. 450,499 filed Dec. 16, 1982. That application is of common assignee herewith, and is incorporated herein by reference. Although the control system disclosed is an advance in the art, it is known now that it does not provide adequately for cleaning the contacts of the tank thermostat. Thus, there remains a need in the art for such a control system which does provide adequately for cleaning the contacts of the tank thermostat.